1. Field of the Invention
The present invention relates to a wire bonding apparatus and, in particular, to a wire bonding apparatus equipped with a structure for reducing inertia during operation in a Z-direction rotating portion including a wire clamp.
2. Description of the Related Art
FIG. 1 is a plan view showing an example of a conventional wire bonding apparatus (wire bonder). A wire bonding apparatus 19 comprises an XY stage (not shown), a base 18 mounted on the XY stage, a rotating arm rotating (swinging) around the rotation spindle 10 with respect to the base 18, a Z-axis VCM (voice coil motor) 9 provided at behind side of the rotating arm 1, and a wire clamp 20 provided at front side of the rotating arm 1.
The wire clamp 20 comprises a stationary clamp member 5 extending at front side of the rotating arm 1, a movable clamp member 6 rotatable around a pivot 8 with respect to the stationary clamp member 5 and adapted to grip a gold wire 4 between the forward end portion of the movable clamp member 6 and the forward end portion of the stationary clamp member 5, and a clamping VCM movable coil 7 having a protruding member protruding from or retracting into a coil main body secured to the stationary clamp member 5.
FIG. 2 is a side view of FIG. 1. From a below part of the rotating arm 1, there is provided a bonding tool 3 extending parallel to the clamp members 5 and 6, and a capillary 2 is secured to the forward end portion of the bonding tool 3. In this wire bonding apparatus 19, when the movable clamp member 6 rotates with respect to stationary clamp member 5 through expansion and contraction of the clamping VCM movable coil 7, the thin gold wire 4 as the bonding wire inserted into the capillary 2 is gripped or released by the forward end portions of the clamp members 5 and 6. When necessary, the rotating arm 1 rotates at a high speed around the rotation spindle 10 by the driving of the Z-axis VCM 9, with the Z-direction rotation portion including the wire clamp 20 and the bonding tool 3 being mounted thereon.
FIG. 3 is a diagram showing an operational sequence of the conventional wire bonding apparatus. First, in a state in which the gold wire 4 passed through the capillary 2 is not gripped by the wire clamp 20, the Z-direction rotation portion including the wire clamp 20 and the bonding tool 3 is lowered at a high speed (a). Further, search on the bonding part is executed in (b), US junction is effected in (c), a predetermined amount of the gold wire 4 is reversed in (d), loop-up is effected in (e), and then loop-down is effected in (f).
Next, a second search is executed in (g), and a second bonding (US junction) is effected in (h). Subsequently, feed-up is effected in (i), and, in a state in which the gold wire 4 is gripped by the driving of the clamping VCM movable coil 7, a high-speed ascent is effected by the driving of the Z-axis VCM 9 in (j). After cutting the gold wire 4 connected at the second bonding point, sparking is performed and releasing the wire clamp 20, and the gold ball due to the sparking is raised in (k).
As described above, in the wire bonding apparatus 19, the Z-direction rotating portion rotates at a high speed in the Z-direction, so that in order to restrain vibration and realize a high speed rotation, it is important to reduce the inertia as much as possible. However, in the conventional wire bonding 19, particularly the wire clamp 20 in the Z-direction rotating portion has a solid actuator of a relatively large mass like the clamping VCM movable coil 7, or, in some cases, has a force conversion mechanism which is solid and of a large mass, so that there is a limitation to the reduction of inertia.
In view of the above problem in the prior art, it is an object of the present invention to provide a wire bonding apparatus which is of a structure as simple and as light as possible, which substantially reduces the inertia in a Z-direction rotating portion rotating at a high speed in the Z-direction, and which is capable of restraining vibration and realizing a stable high-speed rotation of the Z-direction rotating portion.
To achieve the above object, there is provided, in accordance with the present invention, a wire bonding apparatus which comprises a wire clamp capable of moving horizontally in X- and Y-directions perpendicular to each other in the same plane level and rotatable in Z-direction perpendicular to the X- and Y-directions, and a driving means imparting a wire gripping force to the wire clamp. The wire clamp includes a gripping member for gripping a bonding wire; the gripping member can be varied its shape by a fluid supplied by the driving means.
In the wire bonding apparatus of the present invention, a relatively light gripping member which has only to have the capability of effecting a variation in shape is arranged in the wire clamp, and a fluid supply portion for supplying a fluid having a relatively large mass can be arranged on a section different from the Z-direction rotating portion including the wire clamp being present. Due to this arrangement, the wire clamp is substantially reduced in weight, and the inertia in the Z-direction rotating portion is substantially reduced, making it possible to realize a stable high-speed rotation of the Z-direction rotating portion while restraining vibration.
More specifically, the fluid supply portion for supplying a fluid to the gripping member can be arranged on a section of the base which supports the Z-direction rotating portion including the wire clamp at its different section.
Further, it is also desirable that the wire clamp is equipped with a clamp base member whose forward end is formed as a fork shape, and that the gripping member is provided on one protrusion of the fork shape and has an elastic sack-like member expanding toward the other protrusion through introduction of a fluid. In this case, it is possible to obtain, by a very simple structure, the function of a wire clamp gripping/releasing the wire through introduction of a fluid.
Further, it is desirable that there is provided at the forward end of the clamp base member a plate spring member guiding the elastic sack-like member changing its shape with respect to the clamp base member. This helps to stabilize the variation in the shape of the elastic sack-like member.
Preferably, the elastic sack-like member grips the bonding wire with the other protrusion directly or through the intermediate member. By using intermediate member, it is possible to select the gripping condition in the wire clamp.
Alternatively, it is also desirable for the wire clamp to be equipped with a clamp base member whose forward end portion is formed as a fork shape, and the gripping member is provided on one protrusion of the fork shape. The gripping member includes a cylinder formed in the one protrusion and a piston inserted in the cylinder and stretched out toward the other protrusion by introduction of the fluid.
In this case, due to the simple construction using no elastic sack-like member, it is possible to obtain the function of a wire clamp gripping/releasing a wire through introduction of a fluid.
In another aspect of the present invention, there is provided a wire-bonding apparatus which comprises a wire clamp capable of moving horizontally in X- and Y-directions and rotatable in s Z-direction perpendicular to the X- and Y-directions; and a driving means imparting a wire gripping force to the wire clamp. The wire clamp includes a gripping member for gripping a bonding wire; the gripping member can be varied its shape by a volume of a fluid previously sealed in. The driving means is a means of changing the temperature of the fluid to change the volume of the fluid to generate a wire gripping force.
In the latter wire bonding apparatus of the present invention also, a relatively light gripping member is arranged on the wire clamp, and lightweight heater may be provide on the gripping member. On the other hand, a electric current control portion having a relatively large mass and adapted to supply or cut off electric current to the heater through a lead wire can be arranged in a section different from the Z-direction rotating portion being provided. Therefore, the weight of the wire clamp is substantially reduced, and it is possible to obtain the same effect as that of the former wire bonding apparatus.